Wizards, Aliens, and Starships: Physics and Math in Fantasy and Science Fiction

by Adler, Charles L.

  PART IV

  YEAR GOOGOL

  CHAPTER SEVENTEEN

  THE SHORT-TERM SURVIVAL OF HUMANITY

  17.1 THIS IS THE WAY THE WORLD WILL END

  This section poses a simple question: how long can humanity last? Here I am going to throw caution to the winds: This is not a question that I will try to cast in terms of realistic bounds; instead, I will simply speculate wildly as to how long the laws of physics will let us last. In doing so, I examine the different ways in which the human race can become extinct. I move forward in jumps: first considering all the many, many ways in which we can do ourselves in during the next century or so, then taking up more cosmic catastrophes. From the laws we understand today, if we get lucky, the species could last as long as a googol years.

  17.2 THE SHORT-TERM: MAN-MADE CATASTROPHES

  So, whither humanity? I am greatly indebted to the books Last and First Men and Star Maker and their author, Olaf Stapledon, a British science fiction writer of the 1930s. Both are tour de force looks at the long-term history of life in the cosmos. Last and First Men examines the future of the human race out to a time trillions of years in the future when our descendants have evolved into hyperintelligent giants with telescopes on their heads living on the planet Neptune (it makes sense in context). Star Maker is even more audacious: it attempts to follow the evolution of all life everywhere in the universe, to a time thousands of eons past the end of the human race, and life’s (ultimately fruitless) attempts to make sense of the universe and its creator. Along the way, Stapledon explores the myriad ways in which humanity and other species come to catastrophe and recover (or not) in their struggle upward. The novels, despite being written 80 years ago, are the best examples of “thinking big” in all of science fiction. Among other things, Stapledon invented the idea later christened the Dyson sphere.

  Of course, to survive past the end of all the stars, we need to survive past the end of the century. In the short term, mankind is most likely doomed by… Mankind.

  17.2.1 Nuclear War

  But we can be thankful and tranquil and proud,

  That Man’s been endowed with a mushroom-shaped cloud,

  And we know for certain that one lucky day,

  Someone will set the spark off,

  And we will all be blown away!

  —THE KINGSTON TRIO, “MERRY LITTLE MINUET”

  An all-out nuclear was the odds-on favorite for the demise of the human race when I was a boy. Countless science fiction novels and stories deal with all-out nuclear war, usually between the United States and the late Soviet Union. Of these, On the Beach by Neville Schute is one of the best. It deals with the aftermath of a nuclear holocaust, with a number of survivors waiting for the end as radioactive fallout gradually kills off all life. Most books of this kind were written roughly between 1950 and 1970, when Cold War tensions were at their peak. There are also a number of science fiction novels from this time about aliens coming to Earth and saving us from a nuclear holocaust. The best of these is Childhood’s End, by Arthur C. Clarke, because it presents a nifty twist on the story: the aliens save us, but they are saving us for something else. I won’t say anything more because if you haven’t read this novel, you need to. It’s a bit dated, but it still packs a kick like a mule.

  You used to see bumper stickers that read, “One nuclear bomb can really ruin your day.” The only military use of atomic weapons was at the end of World War II, when the United States used two 10 kt atomic bombs to destroy the cities of Hiroshima and Nagasaki. Estimates vary, but the bombs were responsible for the death of up to 100,000 people in each city. The center of each city was completely destroyed. The human misery caused by the bombing and the radioactive fallout were also staggering; there isn’t enough space here to do it justice, but read the end of the book The Making of the Atomic Bomb by Richard Rhodes for details if you want [197].

  At the height of the Cold War, the combined strength of the nuclear arsenal of the United States and Soviet Union was roughly one million times the power of the Hiroshima bomb. There is an interesting thing about this, however: the radius of complete annihilation of a bomb doesn’t scale as the bomb energy but as its square root. For example, the 10 kt bomb that destroyed Hiroshima could probably wipe out Manhattan, which is about 1 mile long. A 1 megaton hydrogen bomb, 100 times more powerful, wouldn’t wipe out an area with a radius of 100 miles but one with a radius of only about 10 miles, about the size of the five boroughs. Therefore, the combined nuclear arsenal of both powers could directly destroy an area roughly 1,000 miles in radius—big, but not Earth-shattering. I don’t want to trivialize the suffering that would be caused by such a holocaust—far from it. As a teenager living in the D.C. suburbs, I used to stay up nights worrying about the imminent threat of nuclear holocaust. The bombs would be targeted at the major cities where the bulk of humanity lives, so the destructive power would be devastating. Cold War strategists used to estimate the numbers of people killed in terms of “megadeaths”; Dr. Strangelove of the eponymous film is a parody of one of these cold-blooded types. Death estimates for an all-out nuclear war would start in the region of ten million, going to an upper range of over 100 million people killed immediately. And that is to say nothing of the lingering death by radiation poisoning of an equal number of people.

  Yet even given all of this horror, a nuclear war wouldn’t directly kill off everyone on the planet. There are six billion people alive today; perhaps 1 to 10% would be killed off directly or from fallout. The biggest danger of a nuclear holocaust is probably not the destructive power of the bombs themselves, great though it is, nor that of the nuclear fallout, horrifying though that is. It is the danger of nuclear winter.

  Consider the following: the destructive energy in a 10 MT H-bomb is about 4×1016 J. In addition to the heat and shock wave produced by the blast, a large amount of dust and other particulate matter can be lifted high into the stratosphere [97]. The stratosphere, the highest region of the Earth’s atmosphere, begins roughly 100 km above the surface of the Earth. The energy required to lift 1 kg of material into this region is given by the formula

  If only 1% of the bomb energy went into lifting particulates into the stratosphere, then we could expect about 4×107 kg per megaton lifted there. This estimate is pretty crude, so we can’t expect better than an order of magnitude agreement. Most papers on global warming assume a value of about 3×108 kg per megaton. In addition, soot from burning cities and forest fires would add to the total [200]. Such particulates take a long time to settle out of the atmosphere, possibly up to several years, and they act to block sunlight from reaching the Earth. Even a small nuclear war, such as a limited exchange between India and Pakistan, could lower global mean temperatures by nearly 1°C, resulting in large-scale changes in agriculture and possible famine.

  This scenario, refered to as “nuclear winter,” will come back in an altered form in chapter 21, when we talk about the prospects for the longterm survival of humanity. However, if the global climate were altered significantly by a massive nuclear exchange, there is a good chance that a very large fraction of humanity would die as a result of the disruption of agriculture.

  17.2.2 Global Warming

  At the present time, however, the world is in danger of getting too hot, not too cool. Since the breakup of the Soviet Union, fears of all-out nuclear war have more or less died away; there is always the danger of a rogue state or a terrorist group getting its hands on a nuclear bomb, but there is less of a chance that the world will end in a huge holocaust. The world’s nuclear arsenal has been reduced by a factor of three since the breakup of the Soviet Union. In 2010 the Doomsday Clock in the Bulletin of the Atomic Scientists was pushed back from five minutes before midnight—the witching hour—to six. Then in 2012 it went back to five minutes before midnight because of the threat of global climate change.

  Most people have some idea what the phrase “global warming” means. There are in fact three related terms to be understand: �
�global warming,” “global climate change,” and the “anthropogenic greenhouse effect.” In a nutshell, the Earth’s mean temperature seems to be rising as a result of the large-scale production of carbon dioxide (CO2) and other industrial gases by our civilization; this has been going on for about the past 200 years. The International Panel on Climate Change (IPCC) in its 2007 report estimated that the world’s mean temperature will rise somewhere between 2°C and 6°C by the year 2100, with unpredictable consequences for human civilization [223]1.

  A few words before I go on to discuss the science behind anthropogenic (man-made) global climate change. Some seem to think that this theory is somehow controversial, and that not everyone is convinced that it is true. Hogwash! The people who matter, which is to say the people who spend their lives studying this theory (i.e., climatologists), are of almost uniform opinion on the subject. Global warming is real, and it is dangerous. At this point the processes of global warming cannot be reversed (though the effects can be partially mitigated). It is inevitable that the world’s temperature will rise significantly over the next century. The disagreements are only about the details: how much, which parts of the world will be most affected, and so on. The theory is controversial in the same way in which the theory of evolution by natural selection is controversial: accepted by scientists, but not accepted by people who are either scared of the implications of the theory or have a stake in the theory not being true.

  Of course, global climate change has been incorporated into science fiction novels. Kim Stanley Robinson has written a trilogy dealing with the effects of global climate change. The first novel in the trilogy, 40 Signs of Rain, looks at the effects of the Earth passing a “tipping point,” after which civilization begins to deal with the effects of rapid climate change [199].

  We have already discussed the mathematics behind the greenhouse effect on planetary temperatures in chapter 14: suffice it to say here that certain gases in Earth’s atmosphere act to trap heat near the surface of the Earth, raising Earth’s mean temperature though the blanketing effect of these gases in exactly the same way a thick blanket or jacket keeps you warm. The natural greenhouse effect in general is good. Earth would be some 30°C colder than it is now without it, cold enough that ice would cover most of the planet most of the year. However, since James Watt invented the first commercially viable steam engine in 1776, humanity has burned coal and later oil to provide energy for its rapidly expanding industrial civilization. This has increased the CO2 concentration of the atmosphere by about 33% over its preindustrial level. The first scientist to understand that increasing human-created greenhouse gases would lead to increasing mean global temperature was the 1903 Nobel Laureate in Chemistry, Svante Arrhenius [141]. His initial work marks the first important theoretical study of climatology; he did what modern climatologists do, modeling the effects of increased greenhouse “forcing” using a sophisticated geographical model. Unlike modern climatologists, he didn’t have access to modern computers. Calculating the effects of greenhouse forcing by hand took him several years. However, his estimate of warming of a few degrees Celsius is similar to modern estimates. He felt that this would be a good thing in making the world’s climate more tropical; perhaps his optimism stemmed from the fact that he lived in Sweden [141].

  The IPCC predictions are based on sophisticated computer models that do the same sort of calculations Arrhenius did at the turn of the last century. The models divide the world into a three-dimensional grid; horizontal gridding is in squares of a few kilometers on a side, while the atmosphere is considered in terms of vertical layers of about 1 km height. The models look at heat input from the sun, the amount reflected from the surface of the Earth and from atmospheric aerosols and clouds, and the amount trapped by greenhouse gases, plus transport across different layers due to air motion [157, p. 68]. The models are extensively tested against each other and against predictions made to local climate conditions; one test used by most modelers is to examine cooling of the Earth as a result of volcanic eruptions, such as the 1993 Pinatubo explosion and the 2010 Eyjafjallajökull eruption in Iceland.

  In chapter 14 we presented a simple “two-layer” model to estimate the mean temperature of a terrestrial planet, including the greenhouse effect. The layers considered are the planetary surface treated as a whole and the atmosphere, again treated as a whole. There are four inputs to the formula: stellar luminosity, expressed in terms of the luminosity of the Sun; planetary distance, expressed as a multiple of the distance of Earth from the Sun; mean planetary albedo A, the fraction of light reflected from the planetary surface (A = 0.3 for Earth), and the fraction of reradiated heat trapped by the atmosphere, f. For Earth, putting the numbers in the formula results in a mean planetary temperature of

  This highlights the importance of the greenhouse effect for life on Earth. Without warming from atmospheric greenhouse gases, the case when f = 0, the Earth’s mean temperature would be a chilly 254 K, or about −19°C. We can calculate f from Earth’s mean temperature, 288 K, indicating f = 0.77 in this crude model. Of course, this doesn’t tell us what f is due to; that is a pretty involved calculation, as one needs to know the infrared absorption bands of all the important greenhouse gases, which also change with atmospheric concentration and pressure. Modeling these absorption bands is one factor in how complicated the climate modeling programs are. The parameter f depends on greenhouse gas concentrations but is not an additive quantity in this if concentrations become too high. Also, of course, different gases are more or less effective at trapping radiation; for example, methane is twenty times more effective by weight in trapping radiation than CO2 is. However, there is about 300 times more CO2 in the atmosphere than methane, so CO2 contributes about ten times more to global warming than methane does. Water vapor is the most important greenhouse gas, representing some 80% of the total effect, with CO2 being the second most important contributor at roughly 10%. Other types of greenhouse gases contribute a few percent or less.

  I present a simple model to estimate the change in temperature due to a change in the fraction of heat trapped by the atmosphere. Does a 1% increase in absorption mean a 1% temperature increase? No We can use calculus and equation (17.1) to show that

  If f increases by 4%, the global mean temperature will increase by about 1%, or roughly 3°C, since the mean temperature is around 300 K. A very crude estimate of the anthropogenic greenhouse effect can be made as follows: greenhouse warming by CO2 represents about 10% of the total. Since CO2 atmospheric concentration has increased by about 25% since 1800 CE, total greenhouse forcing has increased by about 2.5%. The equation thus predicts an increase in world temperature of about 0.6%, or roughly 2°C. This isn’t bad for a very crude estimate; mean world temperature has risen by somewhere between 0.75°C and 1.5°C since 1800, or about a factor of two off from our crude estimate.

  The effects of global warming are unforseeable in detail but aren’t likely to be good for humanity. Predictions include more and more severe droughts, particularly in areas such as California that are already suffering. Also, we will see more frequent and more violent hurricanes, with corresponding billions of dollars in property damage. The melting of the polar ice caps, sea-level rise, and other unsavory occurrences can also be expected. Major drought in California alone would be very bad news. The worst-case scenario would make large portions of the state uninhabitable and unsuitable for agriculture. Since fully 30% of all of America’s agriculture is in California, this could be a great disaster, with escalating food prices being the least of the problems we could face.

  Lest this seem unthinkable, the United States has experienced a similar if smaller-scale ecological disaster in the last century: in the Oklahoma dust bowl disaster of the 1930s. Overuse of farmland in the western states and a series of droughts led to large-scale topsoil erosion, crop failure, and mass migration of farmworkers out of the worst-affected areas. Combined with the Great Depression, framland drought led to vast human suffering. If I may refer t
o a non-science fiction novel, John Steinbeck’s The Grapes of Wrath is a fictionalized but realistic account of one family dealing with these problems [226]. Recently, with a better understanding of climatic variations, archaeologists have found that climate has played a significant role in history. Jared Diamond’s Collapse and Elizabeth Kolbert’s Field Notes from a Catastrophe have sections reflecting on how climatic change led to the collapse of various historic and prehistoric societies [66][141]. If it’s any consolation, we may be running out of the fossil fuels whose consumption leads to such atmospheric warming.

  17.2.3 Hubbert’s Peak

  For the petroleum industry, the last century has been a period of bold discovery and adventure. Whole petroleum provinces analogous to the continents have been discovered and partly explored; a few tens of very large fields, corresponding to the large islands, and hundreds of small fields, the small islands, have been discovered. But how far along have we come on our way to complete exploration?

  —M. KING HUBBERT, NUCLEAR ENERGY AND THE FOSSIL FUELS

  When I was a lad of eight, I remember waiting in the car for an hour with my mother to buy gas. This was back in 1973, during the short-lived OPEC oil embargo. Many of the Persian Gulf countries had stopped selling oil to the United States because of U.S. support of Israel during the Yom Kippur war. The government instituted gas rationing based on the last digit of the license plate of the car one drove. The embargo didn’t last long, as the United States and the Persian Gulf countries are in a “co-dependent” relationship. But at one point, the United States was the largest oil-producing country in the world, and one of the biggest oil exporters. Now we are seventeenth on the list of oil-producing countries and the single largest oil importer. We produce only about one-fifth of the oil we consume. What happened?